1. Field of the Invention
The present invention relates to an exposure apparatus which projects the pattern of an original onto a substrate, thereby exposing the substrate to light, and a device manufacturing method.
2. Description of the Related Art
In manufacturing micropatterned devices such as a semiconductor device, liquid-crystal device, and micromachine, an exposure apparatus is used to project the pattern of an original (reticle) onto a substrate (for example, a wafer or glass plate), thereby exposing the substrate to light. Examples of the exposure light are visible light, ultraviolet light, EUV light, X-rays, an electron beam, and a charged-particle beam. Examples of a projection system for projecting the pattern of an original onto a substrate are a dioptric system, catoptric system, catadioptric system, and charged-particle lens.
The exposure apparatus is required to accurately align an original stage which holds an original and a substrate stage which holds a substrate. The exposure apparatus is also required to accurately support structures such as an optical system support which supports the projection system, an original stage surface plate which supports the original stage, and a substrate stage surface plate which supports the substrate stage.
Also, the exposure apparatus requires a vibration control device for suppressing any external vibration such as vibration transmitted from bases such as the floor on which the exposure apparatus is installed from being transmitted to, for example, the stages.
To meet this need, the structures such as the surface plates in the exposure apparatus are generally supported by foundation structures such as the floor through a vibration control mount. In this specification, “vibration control” means reducing vibration.
An active vibration control device which detects vibration by a sensor and operates an actuator based on the signal output from the sensor has already been put to practical use. It is a common practice to use, as the actuator for the active vibration control device, an air pressure actuator which regulates the pressure of the internal space of a gas spring, thereby actively controlling a thrust produced by this internal pressure.
To improve a function of reducing the vibration of the structure supported by the vibration control mount, it is effective to decrease the spring constant of the vibration control mount. Then, it is effective to use a gas spring as the vibration control mount. Because a gas spring can easily produce a large thrust by setting its pressure receiving area to be sufficiently large, it can also suitably be used as a support mechanism which supports a heavy structure. Hence, using an air pressure actuator as the actuator for the vibration control mount has a merit that it can also be exploited as the support mechanism, thus attaining a vibration control device having a relatively simple structure (see Japanese Patent Laid-Open No. 11-294520).
Conventionally, when the exposure apparatus is in a normal operative state (including various regulation processes for exposure), a vibration control mount including an air pressure actuator using a gas spring supports a structure in the exposure apparatus with respect to a foundation structure while reducing the vibration of the structure in the exposure apparatus. However, in assembly and regulation of the exposure apparatus, the structure in the exposure apparatus must be supported with respect to the foundation structure with a high rigidity to ensure safety. In this case, not the vibration control mount including a gas spring but a stopper or the like provided separately from the vibration control mount supports the structure in the exposure apparatus. If the exposure apparatus suffers an abnormality and therefore a sufficient amount of driving gas cannot be supplied to the air pressure actuator built in the vibration control mount, the vibration control mount including a gas spring can hardly support the structure in the exposure apparatus. Also in this case, a stopper or the like supports the structure in the exposure apparatus as in the above-described case. The same applies to a case in which signal transmission to the air pressure actuator is disabled or to be stopped.
The support position (the point of action) of the structure in the exposure apparatus changes between when the gas spring supports the structure and when the stopper supports the structure, so its gravitational deformation characteristic changes between the two cases. In one example, the support position changes between when the vibration control mount supports an optical system support which mounts an interferometer and a projection system for the exposure apparatus and when the stopper or the like supports the optical system support, so the deformation characteristic of the optical system support may change on the order of several micrometers.
When a structure in the exposure apparatus mounts two components while being supported by a stopper, and is then supported by a gas spring, the positional relationship between these two components may change. More specifically, when the optical system support mounts a projection system and interferometer while being supported by a stopper, and is then supported by a vibration control mount, the distance between the projection system and the interferometer may change on the order of several micrometers.
Along with the recent increase in the size of the exposure apparatus, the sizes of the structures in the exposure apparatus are also increasing. To decrease the weight of the exposure apparatus, it is necessary to minimize the weights of the structures. To meet this need, the structures in the exposure apparatus are desirably imparted with minimum necessary rigidities while the exposure apparatus is in a normal state, that is, they are supported by vibration control mounts. From this viewpoint, the amount of change in the positional relationship between components due to change in the support position as described above may increase. However, in recent years, considering a demand for a higher accuracy of the exposure apparatus, a change in the positional relationship between components due to change in the support position is non-negligible.
When two components mounted on a structure must be aligned precisely, a process of re-adjusting the positions of the components after mounting them on the structure is necessary. This increases the number of assembly processes and the cost.
The deformation characteristic of a structure in the exposure apparatus changes between when a gas spring supports the structure and when the stopper supports it, so a strain remains in the structure itself or the components mounted on the structure. For example, even when the support position is returned to the original support position, the components may not return to the initial states (for example, the initial position and deformation state) owing to an irreversible effect such as friction. More specifically, when an optical system support mounts a projection optical system while being supported by a stopper, is then temporarily supported by a gas spring, and is supported by the stopper again, the position and deformation state of the projection system may change from the initial state upon mounting.
Along with the recent increase in the accuracy of the exposure apparatus, the number of components in the exposure apparatus is increasing. Considering the limiting condition of the installation space of the exposure apparatus, it is necessary to save the spaces to accommodate the components. This makes it difficult to ensure sufficient spaces to accommodate the stoppers.
Also along with the recent increase in the accuracy of the exposure apparatus, it is demanded to clean the environment in the exposure apparatus and precisely control the temperature in the exposure apparatus. To meet this demand, when a drivable stopper is used, dust, waste heat, and the like released from a stopper driving mechanism to the environment in the exposure apparatus are becoming non-negligible.